1. Field of The Invention
The present invention relates generally to a rotary head drum, such as is commonly used in a video tape recorder (VTR).
2. Description of The Prior Art
A rotary head drum arrangement is well known for use in recording and reading image data in a VTR, for example. Such head drum arrangement generally employs a rotary magnetic head which is part of a motor driven head drum assembly utilized in recording and playback of a video signal to and from magnetic tape. In such an arrangement, a head tip of a magnetic head mounted in the rotary drum, is inclined slightly in respect to the running direction of the tape. With a normal, helical scan type head drum arrangement, image data is recorded on the tape in diagonal bands or tracks.
FIG. 4 shows an example of a rotatable head drum arrangement 1 of a helical scan type which comprises a rotary drum body 10 for rotatably mounting a magnetic head 16 and which defines an outer circumferential surface 10a from which a tip end of the magnetic head 16 projects slightly. The rotary drum body 10 is rotatably mounted on a spindle 21 via bearings 22, which may be ball bearings or the like. The rotary drum body 10 is mounted by way of the spindle 21 on a stationary drum 20 for rotating relative thereto. A rotor 31 is associated with a portion of the rotary drum body 10 and spaced by a predetermined gap from a stator 35 associated with said spindle 21. The rotor 31 and stator 35 comprise main components of a motor 30 for driving the head drum arrangement 1.
Further, during recording or playback operation of the head drum arrangement, a rotary transformer 40 is utilized for transmitting signals to and from the rotary drum body 10. The rotary transformer 40 comprises a transformer member 41 fixed to a lower portion of the rotary drum body 10 and opposing a second transformer member 42 fixed to an upper portion of the stationary drum 20.
Further, a rotary flange 12 is attached around outer races of the bearings 22 and is affixed to a drum base 11 of the rotary drum body 10 by a bolt 13. At a lower side 11a of the drum base 11 a head base member 15 is affixed via a mounting screw 14. At the outer end of the head base member 15, that is, a portion extending to the outer circumference of the cylindrical shaped rotary drum body 10, the magnetic head 16 is mounted. The drum base 11 includes a cut-out 11c at the outer circumferential surface 10a of the rotary drum body 10 for allowing the magnetic head 16 to project therethrough. A pairing adjustment screw 17 is provided in the drum base 11 for exerting downward pressure at substantially a center portion of the head base member 15, and such pressure is adjustable for determining a height of the head 16. An annular terminal plate 18 is associated with the flange 12, and includes an elastic, reverse C-shaped contact portion 19, for electrically connecting the head 16.
The rotor 31 (or yoke) of the motor 30 of the drum assembly 1 is substantially disk shaped, and an upper surface 11b of the drum base 11 receives a bolt 33 therethrough for securing the rotor 31 thereto. The rotor 31 has an annular magnet 32 affixed thereto. Further, the stator 35 (yoke) is associated with a second flange 37 connected to an upper part of the spindle 21. The stator 35, the second flange 37 and a back yoke 34 are secured together by a retaining screw 38. A lower surface of the stator 35 is provided with a coil portion 36, spaced from the magnet 32 with a predetermined clearance therebetween.
The back yoke 34 is a substantially disk shaped cap portion which covers a top portion of the rotary drum body 10. The rotary head drum assembly further includes a terminal plate 39 located at an upper portion of the spindle 21 and coupled with the stator 35. Above the back yoke 34, and also retained by the bolt 38, there are a flexible circuit substrate 50 and a guide protector 51.
The lower, cylindrical stationary drum 20 has an inclined groove 20a formed in the outer circumference thereof for helically guiding magnetic tape (not shown) around the head drum. The stationary drum 20 further includes a lower drum base 20b supporting the fixed transformer member 42. At a lower part of the lower drum base 20b, below the fixed transformer member 42, a pin 23 is coupled with a terminal plate 24 for interconnecting the transformer member 42 with a second flexible circuit substrate (not shown). Furthermore, the lower drum base 20b has a central bore 20c with a diameter which is substantially equal to that of the spindle 21 for firmly retaining the spindle by press fitting thereof.
For head pairing control a threaded opening 11d is provided in the drum base 11 for receiving the pairing adjustment screw 17. The pairing adjustment screw includes a tip end portion 17a exerting downward pressure on the head base 15 which is retained by the mounting screw 14. By this arrangement, the head base may be urged flexibly downward for adjusting the height (pairing) of the head 16.
FIG. 5 shows a conventional head base such as is generally mounted under the drum body 10 of the conventional head drum assembly 1 described above. The mounting screw 14 represents a fixed point, or fulcrum A on FIG. 6, while the head 16 represents a controlled edge B and the point at which the tip end 17a of the pairing adjustment screw 17 applies pressure to the head base 15 represents a leverage point C. As may be seen from FIG. 6, control of head position is effected by applying leverage (pressure) to the leverage point C between the fixed end (fulcrum A) and the controlled edge B for changing the head position. According to this construction, a distance from the leverage point C to the fulcrum A is shorter than a distance from the controlled edge B to the fulcrum A. Thus, during pairing adjustment, the deflection of the controlled edge (L.sub.B) is greater than the deflection of the leverage point (L.sub.C), that is to say, L.sub.B) &gt;L.sub.C. However, in this condition, very fine adjustment such as is required for a 8 mm video cassette recorder for example, cannot be readily accomplished. Further, backlash, etc., of the pairing adjustment screw 17 may occur, causing slippage of a leading edge 16a of the head 16 and, according to the above described construction, accurate pairing adjustment is difficult and time consuming.
Further, as seen in FIG. 5, the head base may mount two heads having predetermined azimuth angles in a so called double azimuth arrangement, and this arrangement presents the same problems as the above described single azimuth arrangement.
Therefore, it has been required recently to provide a small, precisely adjustable rotary head assembly which is capable of very fine adjustments.